Abstract The degradation reaction of CH 2 CN radical with O( 3 P) was firstly studied using quantum chemical methods. The energetics were calculated at CCSD(T)/cc‐pVTZ//B3LYP/6‐311++G(d,p). The formation of the intermediate C‐IM1 (CH 2 C(O)N) is the dominant channel by addition between O( 3 P) and the central‐C atom of CH 2 CN. Due to higher barriers, the terminal‐C‐addition/elimination, N‐addition/elimination, substitution and hydrogen abstraction channels are negligible. The rate constants were calculated by means of the RRKM‐TST theory. The total rate constants revealed positive temperature dependence and pressure independence. The calculated results were in good agreement with the experimental values.